In casting of ferrous and non-ferrous products, metal is melted in a melting furnace. The molten metal is stored in a molten state ready for delivery to the mold. A metered amount of molten metal is delivered to the mold. Several devices have been proposed which will deliver a metered amount of molten metal or a shot to the mold.
An automatic ladling system is described in U.S. Pat. No. 2,846,740 and known as the LINDBERG AUTOLADLE.TM.. The LINDBERG AUTOLADLE.TM. comprises a crucible communicating with a balance tube and a delivery tube. The balance tube communicates with the molten metal of the furnace and the crucible. The delivery tube communicates with the exterior and the crucible for delivery of the shot to the mold cavity. The crucible is initially unpressurized. The molten metal inside the crucible is level with the top of the balance tube. The top of the balance tube is slightly above the maximum level of molten metal within the furnace. Air pressure is forced into the crucible and forces the molten metal through the delivery tube into a launder. The amount of metal delivered is controlled by an adjustable timer. Once a predetermined time period has elapsed, a vacuum is applied to the crucible drawing molten metal from both the balance tube and the delivery tube. Molten metal is drawn into the crucible until its level is above the height of the balance tube. The crucible is then vented to the atmosphere allowing the metal to flow back into the furnace until the level of the molten metal in the crucible is the same as the height of the balance tube.
The LINDBERG AUTOLADLE.TM. will generally deliver adequate amounts of shot to the mold cavity. However in situations where high efficiency is required, the LINDBERG AUTOLADLE.TM. will not provide sufficient accuracy in the delivery of a shot on a consistent and long term basis.
Developments have been made in order to increase the accuracy of the quantity of shot delivered. One such device is described in U.S. Pat. No. 4,220,319. In this device, complicated sequences of varying pressures over predetermined time periods are used. The pressure sequences are designed to compensate for smaller amounts of metal being delivered due to the gradual sinking of the level of molten metal in the dosing chamber. However, such devices become complicated and accordingly become expensive to manufacture and difficult to operate.